The present disclosure relates to a power supply apparatus, a charging method, a rechargeable battery cell unit, and a charging apparatus.
Charging apparatuses such as lithium-ion battery packs that can be repeatedly charged and discharged have been known. Some of these charging apparatuses have a configuration in which rechargeable battery cell units, each of which is formed of a plurality of rechargeable battery cells connected in series, are connected in series. When the charging apparatus is charged and discharged, each of the rechargeable battery cells is also charged and discharged, and thus a charge state of each cell changes. When the charging and discharging are repeated, each of the rechargeable battery cells begins to exhibit a different charge state. If the charging and discharging are continuously repeated in a charge state that varies from one cell to another, the life of the rechargeable battery cells will be shortened. Japanese Patent Document No. 3829453 discloses a method of prolonging the life of rechargeable battery cells by monitoring a charge state of each rechargeable battery cell and controlling, in accordance with the charge state, the charging and discharging of a charging apparatus.
In order to achieve downsizing and cost reduction of a monitoring circuit that monitors a charge state of each rechargeable battery cell, there has been a need to manufacture a monitoring circuit as a large scale integrated (LSI) circuit. To manufacture an LSI monitoring circuit, it is necessary to configure a circuit with, for example, a low-voltage metal-oxide semiconductor (MOS) transistor. If the monitoring circuit is configured as a low-voltage circuit, a voltage to be supplied to the monitoring circuit has to be a low voltage. In order to comply with this, Japanese Patent Application Laid-open No. 2010-124597 discloses a configuration in which the voltage of a rechargeable battery cell unit is reduced in order to supply a stepped-down power supply voltage to a low-voltage driven monitoring circuit.